The present invention relates to a micromirror device of a capacitance type which is used for scanning an optical beam.
Micromirror devices of the capacitance type (hereinafter also referred to simply as “micromirror devices”) have widely been used in various technical fields like optical switches for communication, measuring instruments, scanners, etc. In a micromirror device of the capacitance type, a plurality of electrodes are arranged on a substrate which is placed under a mirror scanning an incident beam. By applying voltage to a proper electrode, electrostatic attraction is caused between the electrode and the mirror and thereby the surface of the mirror is tilted in a desired direction. A typical micromirror device has been disclosed in Japanese Patent Provisional Publication No. 2003-29172 (hereinafter referred to as a “document No. 1”), for example.
In recent years, micromirror devices are being required to secure a wide scan range while achieving miniaturization. To realize a wide scan range, some approaches for increasing the electrostatic attraction for tilting the mirror (enlarging the areas of the electrodes arranged under the mirror, increasing the voltage applied to the electrodes, etc.) can be taken, for example.
However, to realize the miniaturization of the whole device, there is a limit to the enlargement of the areas of electrodes. There is also a limit to the increase of the voltage applied to the electrodes since the load on the mirror surface and ill effects on other elements around the micromirror device increase. Therefore, neither approach is effective for practical use.
Meanwhile, a micromirror device disclosed in Japanese Patent Provisional Publication No. 2003-57575 (hereinafter referred to as a “document No. 2”) aims to miniaturize the whole device and achieves a wide scan range by increasing the electrostatic attraction applied to the mirror by reducing a space between a mirror and electrodes.